First genetic analysis of blood haemoglobin levels and iron content in pork

Pork from modern pig genotypes has a lower iron content compared to pork that was produced in the past. Several studies (Dannenberger et al., 2007; Ruusunen et al., 2004) have shown that a decrease in muscle myoglobin (a source of iron) has inadvertently occurred in pork from lines of faster growing pigs. This myoglobin decrease is the result of a physiological change, specifically an increase in the ratio of white glycolytic fast twitch muscle fibres to red oxidative slow twitch muscle fibres. A decrease in muscle myoglobin results in paler pork. In addition consumers are aware that colour is a quality indicator of fresh pork and overly pale pork is often avoided by discriminating purchasers as it is associated with meat of dubious quality.

Pork haem pigment has been shown to be under genetic control with heritability estimates ranging between 0.17 and 0.39 in different studies (Larzul et al., 1997; Oksbjerg et al., 2004). This suggests that iron depletion in modern pork genotypes can be reversed through genetic selection. Genetic progress can best be achieved by direct measurement upon selection candidates. For meat quality traits such as iron content in pork this is logistically difficult as the animal is required to be slaughtered before muscle iron content can be effectively assayed. For this reason it would be beneficial to develop a measurement technique based upon a correlated trait that can be measured upon live animals. An alternative indirect measure for iron content in pork may be haemoglobin levels in blood.

Data are currently collected with an aim to investigate the genetic control of three iron traits, blood haemoglobin levels at five weeks (HAEM-5) and 22 weeks (HAEM-22) and iron content in pork (IRON-MOL) and to develop appropriate models to estimate variance components for these traits. An additional aim was to determine phenotypic correlations between the three iron traits and other production and carcase measures. First results are presented in these workshop notes describing the haemoglobin and iron content measures along with phenotypic correlations and heritability estimates.